In recent years, the mounting space for electronic parts built in electronic equipment is becoming smaller. For example, there have been many situations where capacitors built in many of electronic equipment must be mounted in a low-profile, small space. Thin film capacitors can be made into lower profiler elements than conventional multi layer ceramic capacitors fabricated by the thick-film processing and facilitate such mounting as described above. Especially, mounting in a place limited in the thickness direction is made possible.
As an example of such thin film capacitors, disclosed in JP Laid-Open Patent Application No. 2004-281446 for example is a thin film capacitor which constructs a dielectric layer containing a dielectric material having a high dielectric constant with Y added as a dopant to (Ba(1−x)Srx)Ti1+zO3+δ, sandwiched by a lower electrode layer and an upper electrode layer. It is preferred that this thin film capacitor contains at least one kind of material selected from a group including transition metals such as Pt, Pd, Au, Ag, Cu, and PtOx, precious metals, conductive oxides, and their combinations or mixtures as the upper electrode layer or the lower electrode layer.
In addition, disclosed in JP Laid-Open Patent Application No. 2006-135036 is a thin film capacitor to be embedded in a printed circuit board. To be specific, provided is a dielectric layer between a first conductive layer used for forming the upper electrode layer and a second conductive layer for forming the lower electrode layer, and the second conductive layer is made a nickel layer or nickel alloy layer. Used as the first conductive layer is copper.
However, these thin film capacitors have a thinner dielectric layer than conventional multi layer ceramic capacitors fabricated by the thick-film method, and were inferior in temperature load test and humidity load test in some cases. In addition, if Cu which is a non-magnetic substance with low resistivity is used as electrode layers of such a thin film capacitor, the equivalent series resistance (ESR) of the capacitor can be decreased, therefore noise can be reduced when used with high frequencies, and preferable characteristics as a capacitor can be obtained. However, according to the investigations by the present inventors, it has become evident that the above-mentioned ill influence on reliability is significant if a metallic material such as Cu is used as the electrode layers.
This invention has been made considering the above-mentioned situation, and its objective is to obtain a thin film capacitor which has sufficient reliability in terms of temperature load test and humidity load test even when Cu is used as the electrode layers of the thin film capacitor and at the same time has a low equivalent series resistance (ESR).